Ivarsonval-tyfe electrical



March 13, 1945; M. J. JOHNSON 2,371,299

DARSONVAL-TYPE ELECTRICAL MEASURING INSTRUMENT Filed Nov. 9, 1945 2Sheets-Sheet 1 (/67? for March 13, -i M. J. JOHNSON EfiflfiD'ARSOliVAL-TYPE ELECTRICAL MEASURING INSTRUMENT 2 Sheets-Sheet 2 FiledNov'. .9, 1943 fave)? Patented Mar. 13, 1945 DARSONVAL-TYPE ELECTRICALMEASURING INSTRUMENT Manfred J. Johnson, New Haven, Conn., assignor TimeCorporation, a corporation of Connecticut Application November 9,1943,SeriaiNo. 509,566 4 Claims. (01. 171 -95) to The United States Thepresent invention relates to improvements in electrical measuringinstruments and relates more particularly to improvements inDArsonval-type electrical measuring instruments, 1. e., electricalmeasuring instruments which include a moving coil and a permanentmagnet. Instruments of the DArsonval-type embodying the presentinvention may have their dials graduated in full amperes, full volts, ormultiples thereof, or the dials may he graduated in decimal or frac-'tional parts of amperes or volts, as is well known in the art. Ininstances where temperatures are measured through the intermediary ofelectrical energy produced (as in a thermocouple), the dials of theinstruments may be graduated in temperature-units. Y

The D-Arsonval-type electrical measuring instruments of the presentinvention are primarily designed for use in conjunction with rectifiers,resistors and other devices, the electro-conductivity of which increaseswith rises in temperature, and vice versa. The effect achieved by meansof the present invention is substantially opposite to that achieved inthe electrical measuring instruments set forth in my co-pendingapplication Serial No. 500,065 filed August 26, 1943.

One ofv the objects of the present invention is to provide a superiorDArsonval-type electrical measuring instrument suitable for use inconjunction with devices which have the characteristic of increasingelectro-conductlvity with increases in temperature, and vice versa, andwhich instrument will automatically compensate for such characteristicsand provide accurat indications, despite marked temperature changes.

Another object of the present invention is to provide a, superiorinstrument of the character referred to. in which simple, reliable andeffective provision is made whereby increases in surrounding temperaturewill automatically cause the moving coil of the instrument to besubjected to lesser flux-densities as the surrounding temperature rises,and viceversa, whereby the instrument may be used in conjunction withrectifiers, resistors. or other devices having the characteristic ofincreased electro-conductivity with increases in temperature, and viceversa. 7 with the above and other objects in view, as will appear tothose skilled in the art from the present disclosure, this inventionincludes all features in the said disclosure which are novel over theprior art and'which are not claimed in any separate application.

tain modes of carrying out. the present invention are shown forillustrative purposes:

Fig. 1 is a view partly in front elevation and partly in section of oneform of D'lArsonval-type measuring instrument embodying the presentinvention;

Fig. 2 is a transverse sectional view taken on the line 2-2 of Fig. 1; vn

Fig. 3 is a diagrammatic view illustrating the electrical connections ofthe particular instrument shown;

- Fig. 4 is aperspective view ing-core; and

Fig. 5 is a perspective view of the permanent magnet.

The particular DArsonval-type electrical measuring instrumentillustrated in the accompanying drawings and chosen for purposes ofmaking clear a preferred form of the present invention, includes alaminated permanent magnet generally designated by the referencecharacter It and having a substantially c shaped'form. The saidpermanent magnet may be made in whole or in part of any suitablepermanent magnet material such as cobalt steel, high carbon steel or anyother suitable permanent-magnet material, and includes two opposedcomplemental pole salients I l. and I2 respectively of oppositepolarities.

0 On the side of the permanent magnet III toward its central aperture I3, the pole salients II and I2 are separated by a gap I, while adjacenttheir respective outer peripheral edges the said pole salients areseparated from each other by a similar gap IS. The end-face of the polesalient ll of the permanent magnet I0 is formed with acylindrically-contoured substantially-semicircular notch l6 facing inopposition to a similar notch ll formed in the end-face'of thecomplemental pole salient l2. Both of the notches l6 and I1 justreferred to'are preferably cylindrically-contoured around a commoncenter lying substantiallypmidway between the complemental pole salientsII and I2.

5 Located centrally in the space provided by the opposed notches l8 andI! in the pole salients II and I! on the permanent magnet II! isa-cylindrically-contoured compensating-core (Fig. 4) generallydesignated by'the reference character It.

of the compensat- 7 The said compensating-core includes a cylindricalinner member l9 and a substantially-tubular band-like outer member 20.The inner member [9 of the compensating-core I8 is preferably formed ofsoft iron or other highly permeable ma- In the accompanying drawings, inwhich cerssterial having substantially no permanent-magnetcharacteristics. The band-like outer member 23 of the compensating-coreI3 is formed of a material of a non-permanent magnet type, thereluctance of which increases as the temperature rises, and decreases asthe temperature falls. Preferably the band-like outer member 20 of thecompensating-core is formed of an alloy comprising about 29% to 33%nickel with a balance substantially all iron. The most preferablecomposition is nickel 30% and iron substantially 10%.

Another material well known in the electrical art and suitable for'usein the makeup of the outer member 20 or its equivalent is an alloycomposed of about 30% copper, about 66 /2% nickel, with the balancesubstantiall of iron. Still another suitable composition having thereluctance characteristics above referred to is an alloy containingabout 9 /2% copper, 88% nickel, with the balance substantially all iron.Stated in other words, the permeability of, the band-like outer member23 of the compensating-core l3 may be said to vary substantiallyinversely with respect to the temperature. In still simpler language itmay be said that the magnetic-conductivity of the outer member 25decreases with a rise in, temperature and vice versa.

The outer member 20 of the compensatingcore I8 is formed with alongitudinal slot 2| re istering with a longitudinal slot 22 formed inthe inner member l9. Extending into and staked in the slots 2| and 22Just referred to, is the inner end of a supporting-plate 23. The outerend of the said supporting-plate 23 is riveted into the central arm orreach 24 of a bracket generally designated by the reference character 25and preferably formed of brass or other nonmagnetic material.

The bracket 25 above referred to includes a bifurcated arm 25 which issecured at its respective opposite ends to the respective front faces ofthe pole salients II and I2 of the magnet l by means of bolts or screws21-21. Opposite its bifurcated arm 25 and extending in parallelismtherewith and hence at a right angle to the central arm or reach 24, thebracket 25 is formed with an arm 28 parallelling the adjacent rear facesof the pole salients II and I2 but spaced outwardly therefrom, as isespecially well shown in FIE. 2.

Mounted in the arm 28 of the bracket 25 but insulated therefrom is arear bearing-screw 23 into the inner end of which fits the conical rearend of a rear stud-like pivot 30. The said studlike pivot 30 is securedcentrally to the rear one of the four walls or reaches ofa'substantiallyrectangular coil-supporting ring or frame 3|.

The said coil-supporting ring 3| is preferably formed of aluminum orother light non-magnetic material and has wrapped therearound aplurality of turns of wire forming what will be termed, for convenienceof description, a coil 32. The said coil 32 will ordinarily be formed ofenameled or otherwise insulated copper wire. The inner or front end ofthe stud-like pivot 3|! is centrally secured to the adjacent rear wallor reach of the coil-supporting ring 3| over the coil 32 in any suitablemanner as, for instance, by a cement of synthetic resin.

Mounted on the front wall or reach of the coilsupporting ring 3|diametrically opposite the pivot 30 and in axial alignment therewith, isa front stud-like pivot 33 generally corresponding to the said pivot 30and cemented or otherwise secured to the said ring over the coil 32. The

conical forward or outer end of the pivot 33 is seated for turningmovement in the rear end of a front bearing-screw 34 which is mounted ina bridge-plate 35 preferably formed of brass or other non-magneticmaterial. The said bridgeplate 35 is secured in spaced relationshipforwardly of the bifurcated arm 25 of the bracket 25 by means of.twoscrews 35-35 and two complemental pillars 31-31. The inner ends of thesaid pillars are rigidly mounted in the bifurcated arm 25 of the bracket25 in any suitable manner.

As thus pivotally mounted the coil-unit, comprising the coil-supportingring 3| together with the coil 32, embraces the compensating-core II,and the opposite side walls or reaches of both the said ring 3| and thecoil 32 are interposed in the ring-like space between the outerperiphery of the said compensating-core l8 andthe concavecylindrically-contoured surfaces of the opposed notches l5 and Hrespectively formed in the pole salients and I2.

Fixedly mounted upon the front pivot 33 of the coil-supporting ring 3|and the coil 32 is a pointer or indicating-member 38 preferably formedof aluminum or other light non-magnetic material and adapted in theusual manner of electrical measuring instruments to sweep over a dial39.

In a manner well known in the DArsonval-type instrument art, two opposedspiral hairsprings 40 and 4| are employed which, in the instance shown,are respectively located adjacent the front and rear pivots '30 and 33.One terminal of the coil 32 is electrically connected through the fronthairspring 40 to the bridge-plate 35 and hence grounded to the permanentmagnet H).

A lead-wire 42 is connected to the permanent magnet as shown in Fig. l,and leads to a terminal-stud 43 mounted in the removable rear wall 44 ofa casing 45 having a crystal 43 at its front. I The remaining terminalof the coil 32 is connected through the rear hairspring 4| to a.regulating lever 41 rotatable about the rear bearingscrew 23 butinsulated therefrom and from the associated parts. A lead-wire 48 hasone end soldered, or otherwise connected, to the regulating lever 41 andleads therefrom to one terminal 43 of a duplex plate rectifier,generally designated by the reference character 53, and mounted withinthe case 45. The said plate rectifier 50 has a complemental terminal 5|which is connected by a lead-wire 52' extending to the terminal-stud 43before referred to and located in the rear wall 44 of the case 45.

The remaining terminal 53 of the rectifier ifl is in the instance shownconnected by a, lead wire 54 to one terminal of a resistor, generallydesignated by the reference character 55, and having its remainingterminal connected by a lead-wire 55 to a terminal-stud 51 mounted inthe rear wall 44 of the case 45 and complementing the terminal-stud 43before referred to.

The plate rectifier 53 may be assumed to be a selenium or similarrectifier having a negative temperature-coefficient, i. e., abilitylargercurrents with increases in temperatur and vice versa.

The resistor 55 will ordinarily include a resistance wire having apositive temperature-coefficient, i. e., the characteristics ofdecreasing electro-conductivity with rises in temperature and vice versasuch, for instance, as a nickelchromium alloy. I

perature-coefllcient as above described, and the to pass resistor 55 andcoil 32 having positive temperature-coefiicient characteristics, itmight appear that these two opposite temperature-coeflicients wouldofiset each other to maintain the accuracy of the instrument.

However, under most conditions the negative temperature-coefficient ofthe rectifier 50 or its equivalent will ordinarily more than oflset thecombined positive temperature-coeflicients of the coil 32 and resistor55 so that more than the proper and predetermined current would passthrough the coil 32 when the temperature rises, thus causing theinstrument to read high at elevated temperatures. This high reading,however, is prevented by the characteristics of the compensating-core I8which decreases in magnetic-conductivity (increases in reluctance) withtemperature rises and vice versa. Thus, when a temperature rise causesthe rectifier 50 or its equivalent to pass a greater'amount of current,the compensating-core i8 will be appropriately proportioned so that itwill coincidentally decrease the flux-density between the pole salientsII and llof the permanent magnet in, with the result that the increasein current in the coil 32 will have proportionately less flux-density toreact upon. This results in substantially correcting the action of therectifier 50 so that the readings of the instrument will remainsubstantially uniform despite marked changes in tem: perature and markedchanges in the amount of current passed by the. rectifier 50 underdifi'erent temperature conditions. I

Conversely, when the temperature of the instrument is lowered, therectifier 50 or its equiv-' alent will pass less current and despite theability of the coil 32 and resistor 55 to pass more current at thislowered temperature, errors would still ordinarily result. The loweringof the temperature however, causes the magnetic-conductivity of thecompensating-core l8 to decrease, thereby providing proportionatelylesser fiuxdensity for the coil 32 to react upon.

Should it be desired for any reason to employ a resistor, such as acarbon resistor having a negative temperature-coefllcient, either aloneor in conjunction with a rectifier having a negativetemperature-coeflicient, the compensating-core l3 or its equivalentmaybe appropriately proportioned to vary the effectiveness of the air gapbetween the pole salients H and I2 and thus automatically compensate forthe effects of temperature changes in other devices to which the coil 32is connected.

The invention may be carried out in other departing from the spirit andessential characteristics of the invention, and the present embodimentsare, therefore, to be considered in all respects as illustrative and notrestrictive, and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein.

I claim: I

1. A DArsonval-type electrical measuring ii strument adapted for use inconjunction with devices having negative temperature-coeflicients,including in combination: a permanent magnet having complementalpole-salients respectively of'opposite polarity; a movable coil-unithaving a movable coil mounted in the field between the complementalpole-salients of the said permanent magnet; indicating-means operativelyconnected to the said movable'coil-unit for actuation thereby; and acompensating-core lospecific ways than those herein set forth withoutcated within the movable coil of the said coilunit and hence within thefield between the complementalv pole-salients of the 'said permanentmagnet, the'said compensating-core increase in the flux-density to whichthe coil of the" said coil-unit is subjected asthe temperature rises andto cause an increase in the flux-density to which the said coil issubjected as the temperature falls.

2. A D'Arsonval-type electrical measuring instrument adapted for use,inconjunction with devices having negative temperature-coeflicients,including in combination: a permanent magnet having complementalpole-salients respectively of opposite polarity; a movable coil-unithaving a movable coil mounted in the field between the complementalpole-salients oi. the said permanent magnet; indicating-meansoperatively connected to the said movable coil-unit for actuationthereby; and a compensating-core located within the movable coil of thesaid coil-unit and hence within the field between the complementalpolesalients of the said permanent magnet, the said compensating-corebeing formed partly of highly-permeable magnetic material and partly ofa magnetic material which decreases in magneticconductivity as itstemperature rises and vice versa,- the said compensating-core beingconstructed and arranged to cause a decrease in the flux-density towhich the coil of the said. coilunit is subjected as the temperature.rises and to cause an increase in the flux-density to which the saidcoil is subjected as the temperature i'alls.

3. A DArsonval-type electrical measuring instrument adapted for use inconjunction with devices, having negative temperature-coeflicients,including in combination: a permanent magnet having complementalpole-salients respectively of opposite polarity; a movable coil-unithaving a movable coil mounted in the field between the complementalpole-salients of the said .perma nent magnet; indicating-meansoperatively connected to the said movable coil-unit tor actuationthereby; and a compensating-core located within the movable coil of thesaid coil-unit and hence within'the field between the complementalpole-salients of the said permanent magnet, the said compensating-coreincluding a substantially-annular member formed of highly-permeablemagnetic material and a second annular member formed of magneticmaterial which decreases in magnetic-conductivity as its temperaturerises andvice versa, the said compensating-core being constructed andarranged to cause a decrease in the flux-density to which the coil ofthe said coil-unit is subjected as the temperature rises and to cause anincrease in the flux-density to which the said coil is subjected as the-temperature falls.

4. A DArsonval-type electrical measuring instrument adapted foruse inconJunction with devices having negative temperature-coefiicients,

' including in combination: .a permanent magnet cated within the movablecoil of the said coilunit and hence within the field between thecomplemental pole-saiients o! the said permanent magnet, the saidcompensating-core including an inner-member formed of highlypermeabiemagnetic material and an outer bandiike member formed of a magneticmaterial which decreases in magnetic-conductivity as its temperaturerises and vice versa, the said c0111- pens'ating-core being constructedand arranged to cause a decrease in the flux-density to which the coilof the said coil-unit is subjected as the temperature rises and to causean increase in the flux-density to which the said coil is sub jected asthe temperature falls.

. MANF'RED J. JOHNSON.

